Experiments on perception without awareness are discussed with special reference to the priming technique. Can response to a second stimulus S2 - of which the subject is aware - be primed by a prior stimulus S1 - masked so as to be unreportable?? Two criteria for lack of awareness of S1 are compared. The first is chance performance on forced-choice S1 identification. The experimental question is clear: Can two response measures (overt report and priming) be dissociated in their sensitivity to the same stimulus information? The second criterion is chance performance on presence-absence judgments concerning S1. While this provides an intuitively appealing criterion for awareness, its use leads to the confounding of two experimental variables. Response measures are different for judgment and priming; but so is the relevant stimulus information. Consideration is given to the consequences of this, and to why presence-absence judgments have such intuitive appeal. Generally, forced-choice identification is to be preferred.